Intriguing detection of $^{12}$CO molecular emission in a classical Be star

TL;DR

This study reports the first detection of $^{12}$CO molecular emission in a classical Be star, revealing new insights into the circumstellar environment and disk evolution of such stars.

Contribution

The paper presents the novel observation of $^{12}$CO emission in a classical Be star, expanding understanding of molecular features in these stars' disks.

Findings

Detected $^{12}$CO emission in 12 Vul for the first time.

Observed variability in hydrogen line profiles indicating disk dynamics.

Proposed scenarios to explain the $^{12}$CO emission in Be stars.

Abstract

In the group of B stars with spectroscopic peculiarities, we can find the Be and the B[e] stars. The Be stars are early-type rapid rotators that present, as their principal characteristic, emission lines of hydrogen and singly ionized metals due to the presence of a gaseous envelope. The B[e] stars present in their spectra heterogeneous features that reveal the presence of regions with very different properties in a gaseous and dusty envelope. Our goal is to study the evolution of the disks around peculiar B stars through the variability of their physical properties and dynamical structure, as well as to set constraints on different models and disk forming mechanisms. Throughout the last decade, we have carried out temporal monitoring of a sample of objects in the near infrared using spectroscopic facilities at the Gemini and Las Campanas Observatories. In the present work, we focus on the classical Be star 12 Vul, for which also optical spectra have been collected quasi-simultaneously. We observed variability in the hydrogen line profiles of 12 Vul, attributed to dissipating and building-up processes of the circumstellar envelope. Also, we found that this Be star presented the $^{12}$CO band heads in emission in one observation. The emission of this molecule has not been previously reported in a Be star, while it is a common feature among B[e] stars. We obtained parameters to describe the $^{12}$CO emitting region and propose different scenarios to explain this intriguing emission.